Using delete notifications to free related storage resources

ABSTRACT

A storage stack delete notification can be received at a storage stack filter. The delete notification can indicate deletion of primary data in a primary storage region. Secondary data that is taking up storage resources managed by the storage stack filter can be identified. The secondary data can be associated with the primary storage region, and the storage resources can be resources other than the primary storage region. It can be determined whether it is useful to have the secondary data continue taking up the storage resources. If having the secondary data continue taking up the storage resources is not useful, then the storage resources can be freed.

BACKGROUND

In computer systems, a storage sub-system may include a storage stackthat includes multiple hardware and software components. For example, atypical stack may include a filesystem as a top component in the stack,one or more storage devices as bottom component(s) of the stack, and oneor more filters between the filesystem and the storage device(s).Storage areas may be represented differently at different levels of thestorage stack. For example, a storage stack may include a storage devicestack that represents storage areas in terms of storage device addresses(e.g., using logical block addressing or cylinder-head-sectoraddressing), whether the storage devices are disks or other types ofstorage devices. On top of the storage device stack, the storage stackmay include a volume stack that represents storage areas in terms oflocations in one or more logical disks or volumes. A volume may cover aportion of a storage device, all of a storage device, or all or part ofmultiple storage devices.

Filters within the storage stack can provide added functionality. Forexample, a snapshot filter can manage snapshots of a volume. As anotherexample, a write aggregation filter can aggregate data to be written toprimary locations in one or more storage devices in a set of lazy writes(i.e., writes that are delayed until an idle or less busy time). Asanother example, the stack may include a disk verification filter thatproduces checksums of data as the data is written to a storage device.The disk verification filter can also compare those checksums withchecksums of the same data as the data is read from the device, therebyverifying the integrity of the data being read. As yet another example,the stack may include a performance-boosting filter that caches data onsome alternative storage media, such as RAM, a USB storage device, orflash media, that is faster than a main storage media. That cached datacan be used to enhance computer performance, such as to more quicklyboot a computer system.

File deletion happens frequently in computer systems. Operating systemprocesses, such as formatting, defragmentation, recycling, temporaryfile deletion, and paging can produce a considerable amount of deletedfile data. However, the information identifying deleted files istypically kept in the filesystem, and is not communicated to a storagedevice that stores the deleted file. As a result, the storage devicetreats both valid data and invalid data (data considered deleted by thefilesystem) in its storage media the same way. Thus, the device performsall necessary operations to maintain the data, even if the data isconsidered invalid by the filesystem. For example, background defectmanagement and error recovery processes may be used for hard diskdrives. Merge, wear leveling and erase may be applied to solid statedevices.

It has been known to send delete notifications, or trim commands, from afilesystem to a storage device to inform the storage device thatparticular blocks or ranges of data have been “deleted” (i.e., theblocks or ranges are now considered to be invalid data). Using thisinformation, storage devices may be able to reduce internal operationson invalid data as a self-optimization. It has also been known to informa storage driver when files are deleted. For example, handshakeoperations between a storage driver and a filesystem could involve thefilesystem informing the storage driver when files get deleted, wherethe driver works with flash storage and does wear leveling operationsfor the storage. The driver could use such notifications to avoidread-modify-writes on deleted files.

SUMMARY

Whatever the advantages of previous tools and techniques, they haveneither recognized the tools and techniques described and claimed hereinfor freeing storage resources related to delete notifications, nor theadvantages produced by such tools and techniques.

In one embodiment, a storage stack delete notification can be receivedat a storage stack filter. The delete notification can indicate deletionof primary data in a primary storage region. Secondary data that istaking up storage resources managed by the storage stack filter can beidentified. The secondary data can be associated with the primarystorage region, and the storage resources can be resources other thanthe primary storage region. It can be determined whether it is useful tohave the secondary data continue taking up the storage resources. Ifhaving the secondary data continue taking up the storage resources isnot useful, then the storage resources can be freed.

In another embodiment, a storage stack delete notification thatindicates a range of invalid data can be received. It can be determinedwhether a write operation is rendered obsolete by the deletenotification. If so, then the write operation can be cancelled.

In yet another embodiment a primary storage region of a storage devicecan store primary data. A secondary storage region that is differentfrom the primary region can store secondary data corresponding to theprimary data. In addition, a storage stack filter can be configured toreceive a storage stack delete notification indicating deletion of atleast a portion of the primary data, and to delete the secondary data inresponse to the delete notification.

This Summary is provided to introduce a selection of concepts in asimplified form. The concepts are further described below in theDetailed Description. This Summary is not intended to identify keyfeatures or essential features of the claimed subject matter, nor is itintended to be used to limit the scope of the claimed subject matter.Similarly, the invention is not limited to implementations that addressthe particular techniques, tools, environments, disadvantages, oradvantages discussed in the Background, the Detailed Description, or theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a suitable computing environment in whichone or more of the described embodiments may be implemented.

FIG. 2 is block diagram of a storage stack in which one or more of thedescribed embodiments may be implemented.

FIG. 3 is a block diagram illustrating a filter modifying an existingdelete notification.

FIG. 4 is a block diagram illustrating a filter creating a new deletenotification.

FIG. 5 is a block diagram illustrating operation of an exemplarysnapshot filter that can implement one or more of the described toolsand techniques.

FIG. 6 is a block diagram illustrating operation of an exemplaryperformance-boosting filter that can implement one or more of thedescribed tools and techniques.

FIG. 7 is a block diagram illustrating operation of a write aggregationfilter that can implement one or more of the described tools andtechniques.

FIGS. 8-10 are block diagrams of circular log files that can be managedby the write aggregation filter of FIG. 7.

FIG. 11 is a block diagram illustrating operation of a volume managerfilter that can implement one or more of the described tools andtechniques.

FIG. 12 is a block diagram illustrating operation of a data verificationfilter that can implement on or more of the described tools andtechniques.

FIG. 13 is a flowchart illustrating a described technique for modifyingan existing delete notification.

FIG. 14 is a flowchart illustrating a described technique for creating anew delete notification with a storage stack filter.

FIG. 15 is a flowchart illustrating a described technique for freeingresources in response to receiving a delete notification.

FIG. 16 is a flowchart illustrating a described technique for cancelingan obsolete data write operation in response to receiving a deletenotification.

FIG. 17 is a flowchart illustrating a described technique for using adelete notification that may apply to an entire storage volume.

DETAILED DESCRIPTION

Described embodiments are directed to techniques and tools for freeingstorage resources related to delete notifications. Such improvements mayresult from the use of various techniques and tools separately or incombination.

Such techniques and tools may include receiving a storage stack deletenotification at a storage stack filter, the delete notificationindicating a primary storage region available for deletion. The storagestack filter can identify data that is taking up storage resourcesmanaged by the storage stack filter, and that is associated with theprimary storage region. Examples of data that is associated with aprimary storage region include data that is redundant of data stored inthe primary storage region, data that is planned to be stored in theprimary storage region in the future, verification data for the datastored in the primary storage region, and metadata corresponding toprimary data stored in the primary storage region. The resources may be,for example, storage space where the data is currently stored, plannedwrite operations for writing the data, or ongoing write operations forwriting the data. The filter can also determine whether it is useful tohave the data continue taking up the storage resources. For example, ifthe data is secondary data that is only used in conjunction with primarydata and the primary data has been deleted, then the secondary datawould not need to be accessed in normal computing operations and itwould not be useful to have the secondary data take up storage space orplanned or ongoing write operations. Accordingly, planned or ongoingwrite operations would be rendered obsolete because there would be noneed to access the data being (or planned to be) written. If the storagestack filter does not need the data to continue taking up the storageresources, then the filter can free the resources. For example, thefilter can free storage space or cancel planned or ongoing data writingoperations.

Accordingly, one or more substantial benefits can be realized from thetools and techniques described herein, including freeing up storageresources.

The subject matter defined in the appended claims is not necessarilylimited to the benefits described herein. A particular implementation ofthe invention may provide all, some, or none of the benefits describedherein. Although operations for the various techniques are describedherein in a particular, sequential order for the sake of presentation,it should be understood that this manner of description encompassesrearrangements in the order of operations, unless a particular orderingis required. For example, operations described sequentially may in somecases be rearranged or performed concurrently. Techniques describedherein with reference to flowcharts may be used with one or more of thesystems described herein and/or with one or more other systems.Moreover, for the sake of simplicity, flowcharts may not show thevarious ways in which particular techniques can be used in conjunctionwith other techniques.

Exemplary Computing Environment

FIG. 1 illustrates a generalized example of a suitable computingenvironment (100) in which one or more of the described embodiments maybe implemented. For example, one or more such computing environments caninclude a storage stack that implements enhancements using deletenotifications. These enhancements could include, for example, usingdelete notifications that may apply to an entire storage volume,modifying delete notifications with filters in the storage stack, and/orusing delete notifications to free related storage resources. Generally,various different general purpose or special purpose computing systemconfigurations can be used. Examples of well-known computing systemconfigurations that may be suitable for use with the tools andtechniques described herein include, but are not limited to, serverfarms and server clusters, personal computers, server computers,hand-held or laptop devices, multiprocessor systems,microprocessor-based systems, programmable consumer electronics, networkPCs, minicomputers, mainframe computers, distributed computingenvironments that include any of the above systems or devices, and thelike.

The computing environment (100) is not intended to suggest anylimitation as to scope of use or functionality of the invention, as thepresent invention may be implemented in diverse general-purpose orspecial-purpose computing environments.

With reference to FIG. 1, the computing environment (100) includes atleast one processing unit (110) and memory (120). In FIG. 1, this mostbasic configuration (130) is included within a dashed line. Theprocessing unit (110) executes computer-executable instructions and maybe a real or a virtual processor. In a multi-processing system, multipleprocessing units execute computer-executable instructions to increaseprocessing power. The memory (120) may be volatile memory (e.g.,registers, cache, RAM), non-volatile memory (e.g., ROM, EEPROM, flashmemory), or some combination of the two. The memory (120) storessoftware (180) implementing enhancements using delete notifications.

Although the various blocks of FIGS. 1-17 are shown with lines for thesake of clarity, in reality, delineating various components andflowchart blocks is not so clear and, metaphorically, the lines wouldmore accurately be grey and fuzzy. For example, one may consider apresentation component such as a display device to be an I/O component.In addition, processors have memory. The inventors hereof recognize thatsuch is the nature of the art and reiterate that the diagram of FIG. 1is merely illustrative of an exemplary computing device that can be usedin connection with one or more embodiments of the present invention.Distinction is not made between such categories as “workstation,”“server,” “laptop,” “handheld device,” etc., as all are contemplatedwithin the scope of FIG. 1 and reference to “computer,” “computingenvironment,” or “computing device.”

A computing environment (100) may have additional features. In FIG. 1,the computing environment (100) includes storage (140), one or moreinput devices (150), one or more output devices (160), and one or morecommunication connections (170). An interconnection mechanism (notshown) such as a bus, controller, or network interconnects thecomponents of the computing environment (100). Typically, operatingsystem software (not shown) provides an operating environment for othersoftware executing in the computing environment (100), and coordinatesactivities of the components of the computing environment (100).

The storage (140) may be removable or non-removable, and may includesolid-state storage devices, magnetic disks, magnetic tapes orcassettes, CD-ROMs, CD-RWs, DVDs, or any other medium which can be usedto store information and which can be accessed within the computingenvironment (100). The storage (140) stores data, such as instructionsfor the software (180).

The input device(s) (150) may be a touch input device such as akeyboard, mouse, pen, or trackball; a voice input device; a scanningdevice; a network adapter; a CD/DVD reader; or another device thatprovides input to the computing environment (100). The output device(s)(160) may be a display, printer, speaker, CD/DVD-writer, networkadapter, or another device that provides output from the computingenvironment (100).

The communication connection(s) (170) enable communication over acommunication medium to another computing entity. Thus, the computingenvironment (100) may operate in a networked environment using logicalconnections to one or more remote computing devices, such as a personalcomputer, a server, a router, a network PC, a peer device or anothercommon network node. The communication medium conveys information suchas data or computer-executable instructions or requests in a modulateddata signal. A modulated data signal is a signal that has one or more ofits characteristics set or changed in such a manner as to encodeinformation in the signal. By way of example, and not limitation,communication media include wired or wireless techniques implementedwith an electrical, optical, RF, infrared, acoustic, or other carrier.

The tools and techniques can be described in the general context ofcomputer-readable media. Computer-readable media are any available mediathat can be accessed within a computing environment. By way of example,and not limitation, with the computing environment (100),computer-readable media include memory (120), storage (140), andcombinations of the above.

The tools and techniques can be described in the general context ofcomputer-executable instructions, such as those included in programmodules, being executed in a computing environment on a target real orvirtual processor. Generally, program modules include routines,programs, libraries, objects, classes, components, data structures, etc.that perform particular tasks or implement particular abstract datatypes. The functionality of the program modules may be combined or splitbetween program modules as desired in various embodiments.Computer-executable instructions for program modules may be executedwithin a local or distributed computing environment. In a distributedcomputing environment, program modules may be located in both local andremote computer storage media.

For the sake of presentation, the detailed description uses terms like“determine,” “choose,” “receive,” “send,” “pass,” and “operate” todescribe computer operations in a computing environment. These and othersimilar terms are high-level abstractions for operations performed by acomputer, and should not be confused with acts performed by a humanbeing, unless performance of an act by a human being (such as a “user”)is explicitly noted. The actual computer operations corresponding tothese terms vary depending on the implementation.

Delete Notification Enhancement System and Environment

A. Storage Stack In General

FIG. 2 is a block diagram of a storage stack (200) in conjunction withwhich one or more of the described embodiments may be implemented. Thestorage stack (200) can include software and/or hardware components. Forexample, the storage stack (200) can include a top-level filesystem(210) and a bottom level storage device (220), as well as storage stackfilters (230) between the filesystem (210) and the storage device (220).The term storage stack filter is used herein to refer to any componentbetween a filesystem and a physical storage medium in a storage device,where the component can receive and pass on read and/or write requests(235) and provide additional functionality. The storage stack (200) mayinclude a logical disk functionality that represents storage units tothe file system in terms of storage volumes, where each volume mayrepresent a single storage device, part of one or more storage devices,or multiple storage devices. If so, then the storage stack can include avolume stack (240), which can provide this functionality, and canprovide additional functionality. A device stack (250) can be positionedbelow the volume stack, and can represent storage positions to thevolume stack (240) in terms of positions within the storage device(220). The storage device (220) can also be considered to be part of thestorage stack (200).

The storage stack (200) could be configured in other ways in otherimplementations. For example, in some implementations volumes alwayscoincide with storage devices, such as in a basic disk configuration. Insuch a configuration, the storage stack (200) may not need to convertstorage positions between volume space and device space. On oneimplementation, the filesystem (210), the volume stack (240), and thedevice stack (250) are all part of an operating system. However, thestorage stack (200) could be configured in some other manner. Forexample, some of the storage stack (200) could be included in a storagedevice itself. As another example, the storage stack could includeprogram modules that are part of applications other than an operatingsystem. Moreover, there could be one or many filesystems, disk and/orvolume stacks and devices interacting with each other in the storagestack.

As an example of how storage positions can be represented in thedifferent layers of the storage stack (200), consider a situation wherea 50-megabyte file is written to a storage device. The filesystem (210)can receive a request (235) to write the file, such as from anapplication, an operating system service, and/or user input. Thefilesystem (210) can then determine an appropriate position in thevolume to store the file. To do this, a filesystem (210) typicallytracks occupied space that contains valid data, which the filesystem(210) may need to retrieve at some point. The filesystem (210) alsotypically tracks free space that contains invalid data, where either nodata has been stored by the operating system or where data has beendeleted (i.e., de-allocated) by the filesystem (210). In oneimplementation, the filesystem (210) can maintain a freespace bitmapfile that can represent free space in a storage volume as 1's andoccupied space in a storage volume as 0's. If megabytes 974 through 1024of the volume are freespace in the freespace bitmap file, then thefilesystem (210) can pass a write request (235) down the storage stack(200) with the data for the file to be written, specifying that thedata-to-be-written is to be stored in megabytes 974 through 1024 of thevolume. That request (235) can be passed down the volume stack (240) andthe volume stack (240) can convert the request (235) from volume spaceto device space.

For example, if a volume spans two storage devices, including onegigabyte of a first device (megabytes 0 through 999 of the volume) andone gigabyte of a second device (megabytes 1000 through 1999), then thevolume stack could split the request into two write requests: one towrite the first 25 megabytes of the file on megabytes 975 to 999 of thefirst device and one to write the last 25 megabytes of the file onmegabytes 0 to 24 of the second device. That request can then be passeddown the device stack (250) and to the storage device (220). Of course,the storage device (220) can include its own internal stack of softwareand hardware components (such as additional storage stack filters) thatcan be part of the storage stack (200), and the device (220) may includeseveral physical storage mediums (e.g., several disks within a diskdrive).

The filesystem can “delete” a file by switching occupied spacecorresponding to the file to freespace, such as in the freespace bitmap.As noted above, this filesystem deletion can be done without notifyingthe storage device (220) or the other components of the storage stack(200). However, it can be advantageous to send a delete notification(260) down the storage stack (200) when the filesystem (210) deletes afile. This notification (260) can specify a region of the volume thatthe filesystem (210) has deleted (i.e., switched to freespace). Thestorage device (220) can use this notification to provide improvedinternal performance and efficiencies, such as by ceasing to maintainthe invalid data in the specified region.

The storage stack filters (230) of the storage stack (200) can also usesuch delete notifications to provide additional enhancements. Forexample, storage stack filters (230) in the storage stack (200) canmodify delete notifications to exclude data being protected by thosefilters (230). For example, referring to FIG. 3, a filter (310) canreceive and modify one or more existing delete notifications (320) toproduce one or more modified delete notifications (330). Referring backto FIG. 2, as another example, storage stack filters (230) can modifydelete notifications (260) to notify lower level storage stackcomponents, including the storage device (220), that data has beendeleted (i.e., de-allocated). As another example of modifying a deletenotification, referring to FIG. 4, a filter (410) can create a newdelete notification (430). This can either be done directly by thefilter (410), or indirectly by the filter (410) instructing some othersoftware or hardware component to create the new delete notification(430).

Referring back to FIG. 2, as another example of an enhancement using adelete notification, filters (230) can use a delete notification (260)to identify storage resources that are not needed and can be freed. Asyet another example, the delete notification (260) can include a flag(265) indicating whether the notification (260) applies to an entirevolume, and one or more of the filters (230) can react differently tothe notification (260) when the notification (260) applies to the entirevolume.

B. Storage Stack Components

Referring still to FIG. 2, some exemplary components of the storagestack (200) will be described. As is indicated by the vertical lineswith arrow tips between the components in FIG. 2, each component can beconfigured to communicate with the component directly above it anddirectly below it in the storage stack (200). The components may alsoinclude interfaces, such as user interfaces, to send and receiveinstructions and other communications between the component and othersoftware or hardware components inside or outside the storage stack(200). The volume stack (240) can include, from top to bottom, asnapshot filter (270) (below the filesystem (210)), aperformance-boosting filter (272), a write aggregation filter (274), anencryption filter (276), and a volume manager filter (278). The devicestack (250) can include, from top to bottom, a partition manager filter(280) (below the volume manager filter (278)), a device stack functionaldevice object (282), a data verification filter (284), and port driver(288) (above the storage device (220)). However, the storage stack (200)could include fewer components, additional components, and/or componentsthat behave differently or are positioned elsewhere in the storage stack(200).

1. Snapshot Filter

The snapshot filter (270) can manage volume snapshots, and can alsofunction as a functional device object (FDO) for the volume stack (240).The FDO for the volume stack (240) can provide the functionality for thevolume. Filters below the FDO but above a physical device object (PDO)in a stack are typically considered lower level filters, while filtersabove the FDO in a stack are typically considered upper level filters.Managing volume snapshots can include taking snapshots of a storagevolume at a particular point in time. This allows users and/or programsto go back in time to the storage volume as the volume existed when thesnapshot was taken.

Managing snapshots could be done by making a copy of an entire volume ata point in time and not allowing any modifications to that copy.Referring to FIGS. 2 and 5, it is typically more efficient to maintainsnapshots by only copying those regions of the primary storage volume(510) where changes have taken place since the time of the snapshot.These copies of the modified regions can be saved in one or moredifferencing files (520). According to this technique, if a region ofprimary data that is subject to a snapshot has not yet been copied, thensuch a region and the primary data stored in the region can be protectedby the snapshot filter (270).

If the snapshot filter (270) receives a write request from thefilesystem (210) to write data to a protected region, then the snapshotfilter (270) can copy the data in the protected region of the primarystorage (510) to the differencing file (520). Then, the data in theprimary storage region (510) can be marked as unprotected, and thesnapshot filter (270) can pass the write request down the storage stack(200). Thus, the snapshot filter (270) can maintain a copy of the datafor an entire volume as the volume existed at the time of the snapshot,with some of the data being stored with the primary data (where theprimary data has not been altered since the time of the snapshot) andsome of the copy being stored in one or more differencing files (wherethe primary data has been altered since the time of the snapshot).

As noted, the snapshot filter (270) can include one or more maps (530)to track which regions of the primary storage region (510) are protected(because the regions are covered by a snapshot and have not yet beencopied to a differencing file) and which are unprotected (because theregions are not covered by a snapshot or have been copied to adifferencing file). For example, for each snapshot, the snapshot filter(270) can maintain a bitmap (530) showing which regions are protected orunprotected by that snapshot, such as with 1's representing unprotectedregions and 0's representing protected regions for that snapshot. Thesebitmaps (530) can be examined to determine whether a region is protectedand needs to be copied prior to data being written to the region.

When the snapshot filter (270) receives a delete notification (260), thesnapshot filter (270) can determine whether a range of data that thedelete notification indicates is being deleted overlaps with a range ofprotected primary data. If there is an overlap, then the snapshot filter(270) can copy the protected primary data to a differencing file (520)prior to passing the delete notification (260) down the storage stack(200). However, the copied data in the differencing file (520) takes upstorage space, and the copy operation can also take up storageresources, including processing resources.

Accordingly, instead of copying the protected data that overlaps withthe range of the delete notification (260), the snapshot filter (270)can modify the range of the existing delete notification (260) toexclude the portion of the range that overlaps with the protected datarange. This could result in the modified delete notification having onecontiguous contracted range or a contracted range that includesdisconnected sub-ranges. The modified delete notification could be inthe form of a single notification or multiple notifications. Themodified delete notification with the contracted range can then bepassed down the storage stack (200) to the performance-boosting filter(272).

As an example, if the existing delete notification (260) applies to arange of 100 megabytes to 200 megabytes of a volume, and a range of 50megabytes to 150 megabytes of the volume is protected, then the snapshotfilter (270) can modify the delete notification (260) to have acontracted range of 151 megabytes to 200 megabytes. As another example,if the existing delete notification (260) applies to a range of 100megabytes to 200 megabytes of a volume, and ranges of 120 to 145megabytes and from 160 to 165 megabytes of the volume are protected,then the snapshot filter (270) can modify the delete notification (260)to have a contracted range including sub-ranges of 100 to 119 megabytes,from 146 to 159 megabytes, and from 166 to 200 megabytes. The entirecontracted range could be included in a single modified deletenotification with sub-ranges or each sub-range could be included in aseparate modified delete notification.

The modified delete notification(s) can be passed down the storage stack(200) to the performance-boosting filter (272). Thus, the protected datawill not be modified in response to the delete notification (260), andthe protected data will not need to be copied at that time. Similartechniques could be used by other storage stack filters that need toprotect data that can be covered by a delete notification (260).

Snapshots may be deleted in some implementations. For example, snapshotsmay be deleted manually by a user, or automatically. For example, a usercan configure the snapshot filter (270) so that the snapshot data(secondary data corresponding to the primary data at the time of thesnapshot, such as the data in the differencing file(s) (520)) takes uponly a certain percentage of the storage volume. For example, if a userspecifies a maximum of fifteen percent, then as the amount of snapshotdata approaches fifteen percent of the storage volume, the snapshotfilter (270) can delete snapshots according to a scheme, such asdeleting the oldest snapshots. At that time, the snapshot filter (270)can inform the filesystem (210) that differencing files (520) that wereused only by the deleted snapshots contain invalid data and can bedeleted. In response, the filesystem (210) can mark the storage regionsof those differencing files (520) as invalid data and send deletenotifications for those regions down the storage stack (200).

In addition, when a snapshot is deleted, the snapshot filter (270) canissue additional delete notifications for primary storage regions (510)that the snapshot filter (270) had omitted from previous deletenotifications (260) because the notifications (260) indicated deleteregions that overlapped with protected regions being protected by thesnapshot filter (270). If those regions are no longer protected afterthe snapshot is deleted, then the snapshot filter (270) can send downthe delete notifications for those regions. This can free up storageresources in the same manner as other delete notifications issued by thefilesystem (210).

The snapshot filter (270) could identify these regions by tracking allregions where delete notifications (260) were withheld or modified bythe snapshot filter (270) because the notifications (260) indicatedranges that overlapped with protected data. However, the snapshot filter(270) can compute regions that can be deleted in another manner, withouttracking those regions. When a snapshot is deleted, the snapshot filter(270) can calculate the product of all the bitmaps (530) that trackunprotected areas for active snapshots after the snapshot deletion. Thisproduces an ignorable product bitmap that shows all storage regions thatare unprotected by the snapshot filter (270) after the snapshotdeletion, such as by having 1's for those regions. The snapshot filter(270) can also take the product of that ignorable product bitmap and thefilesystem's freespace bitmap to produce a bitmap that shows areas thatare considered freespace by the filesystem (210) and are unprotected bythe snapshot filter (270), such as by having 1's corresponding to suchareas. The snapshot filter (270) can create new delete notifications forall such areas and pass the new delete notifications down the storagestack (200) to the performance-boosting filter (272).

If the snapshot filter (270) receives a delete notification (260) with aflag (265) indicating that the delete notification (260) applies to theentire volume, then the snapshot filter (270) can react differently thanit would to a delete notification (260) that applies to less than theentire volume. For example, if the snapshot filter (270) receives adelete notification (260) with a flag (265) indicating that the deletenotification (260) applies to the entire volume, then the snapshotfilter (270) can delete all snapshots for the volume, and the snapshotfilter (270) can disable itself. The snapshot filter (270) can continueto be disabled until it is re-enabled, such as by a user or anothercomputing component. For example, the snapshot filter (270) may bere-enabled the next time a snapshot is created automatically or inresponse to user input.

2. Performance Boosting Filter

Referring to FIGS. 2 and 6, the performance-boosting filter (272) cancommunicate with the snapshot filter (270) above it and the writeaggregation filter (274) below it to receive and pass on deletenotifications (260) and read/write requests and data (235). In addition,the performance boosting filter can copy parts of a primary storageregion (610) into a cache (620) on some other media that is faster thanthe primary storage device (e.g., the other media may be RAM, USB drive,or flash media if the primary storage volume is on one or more harddisks). The data can be read from the cache (620) instead of the primarystorage (610) to enhance system performance. For example, the storeddata may be instructions that are used when booting a computer system,thereby speeding the boot process.

The performance-boosting filter (272) could pass on delete notifications(260) without taking other actions. If a delete notification (260)applies to a region of primary storage (610) that corresponds to thecache (620), then the cache (620) can get out of sync with the primarydata. That would likely not affect the integrity of the cache databecause there would be no reason for the cache data corresponding to thedeleted primary data to be read in the future. However, space in thecache (620) is often quite limited, especially in the types of fastermedia mentioned above. For example, in some implementations the cache(620) may be limited to about 300 megabytes. Thus, it can beadvantageous for the performance-boosting filter (272) to determinewhether data in the cache (620) corresponds to data in primary storage(610) covered by a delete notification (260), and if so theperformance-boosting filter (272) can delete the corresponding cachedata. This can include the performance-boosting filter (272) issuing adelete notification for the cached data or merely marking the deletedregion of the cache as invalid so that more cached data can be stored inthe region. In addition to freeing up resources, such deletions can bebeneficial if the cache (620) needs to be matched to the correspondingareas of the primary storage (610).

If the performance-boosting filter (272) receives a delete notification(260) with a flag (265) indicating that the delete notification (260)applies to the entire volume, then the performance-boosting filter (272)can react differently than it would to a delete notification (260) thatapplies to less than the entire volume. For example, if theperformance-boosting filter (272) receives a delete notification (260)with a flag (265) indicating that the delete notification (260) appliesto the entire volume, the performance-boosting filter (272) can disableitself, or it can remain enabled, but start caching operations fromscratch. If the performance-boosting filter (272) is disabled, it mayremain disabled for a set period of time or until it is re-enabled by anaction of another program and/or user input.

3. Write Aggregation Filter

The write aggregation filter (274) can communicate with theperformance-boosting filter (272) above it and the encryption filter(276) below it to receive and pass on delete notifications (260) andread/write requests and data (235). In addition, the write aggregationfilter (274) can provide the additional functionality of managing writeaggregation and lazy writes of aggregated write requests. When data iswritten to primary storage (710) on the storage device (220), the writeoperation may involve making updates in several different primary datalocations in the volume. Instead of always writing data-to-be-written tothe primary storage locations at the time the requests are made, thewrite aggregation filter (274) can write the data-to-be-written to oneor more log files (720). The write aggregation filter (274) can alsoupdate an in-memory map (730), which can be a table that correlates theprimary locations of the data-to-be-written with the positions of thedata-to-be-written in the log file. The log file (720) can be stored inthe same volume as the primary storage (710) or elsewhere. Thedata-to-be-written can be drained from the log file (720) to the primarylocation(s) in the primary storage (710) in lazy write operations, whichcan be done at idle times, when the storage device (220) would otherwisebe idle. The in-memory map (730) can be examined to determine whichdrain operations still need to be done. After data is drained from thelog file (720), entries in the in-memory map (730) that correspond tothe drained data can be removed.

If read requests for locations of the data-to-be-written in primarystorage (710) come down the storage stack (200) beforedata-to-be-written is drained from the log file (720), the writeaggregation filter (274) can use the in-memory map (730) to redirect therequests to the appropriate places in the log file (720). After thedata-to-be-written is drained to its primary locations in primarystorage (710), the write aggregation filter (274) can allow readrequests for that data to be passed down the stack unmodified.

Referring to FIGS. 7-10, the log file (720) can be a circular file,where a log file storage region (800) is allocated for the log file(720). Data-to-be-written can be added to the log file (720), whichmoves through the storage region (800) as data-to-be-written is added toand drained from the log file (720). Specifically, data-to-be writtencan be added to a “head” (820) of the log file (720) when write requestsare made during busy times, and the data-to-be-written can be drainedfrom a “tail” (830) of the log file (720) when lazy writes are made,such as at idle times. When the head (820) reaches the end of thestorage region (800), data can continue to be written at the beginningof the storage region (800), so long as the beginning has been drained.In this way, the log file (720) can travel a “circular” path through thestorage region (800). As data is added to the head (820) or drained fromthe tail (830), the in-memory map (730) can be updated.

As an example, the log file storage region (800) may be 5 gigabytes.Initially, data-to-be-written can be added to the log file (720), alongwith corresponding metadata describing the primary locations for thedata-to-be-written, starting at a 0 byte marker and continuing toward a5 GB marker. For example, 2 gigabytes may be added, so that the log file(720) extends from the 0 byte marker to the 2 gigabyte marker, and anunused area (812) extends from the 2 gigabyte marker to the 5 gigabytemarker, as is illustrated schematically in FIG. 8.

At idle time, some of the data-to-be-written may be drained from thetail (830) of the log file (720). For example, 500 megabytes may bedrained so that the tail (830) moves forward to the 500 megabyte marker,leaving an additional unused area (912) (that is also part of the unusedarea (812)), as illustrated in FIG. 9.

Adding and draining data can continue until the head wraps around to thebeginning of the log file storage region (800). This is illustratedschematically in FIG. 10, where the tail (830) has moved forward to the3.5 gigabyte marker and the head (820) has moved forward to the 1.5gigabyte marker. Accordingly, the log file (720) begins at the tail(830) and wraps around to the head (820), leaving an unused area fromthe 1.5 gigabyte marker to the 3.5 gigabyte marker.

Referring back to FIGS. 2 and 7, if the write aggregation filter (274)receives a delete notification (260), the write aggregation filter (274)can check the in-memory map (730) to determine whether the regions ofthe primary storage (710) covered by the delete notification (260)overlap with the primary locations of any correspondingdata-to-be-written that is stored in the log file (720). If so, thenthose areas can be trimmed from the in-memory map (730), so that areasassociated with the delete notification (260) will not be drained to theprimary storage (710), and storage resources (storage device, processorsthat can be used for storage operations, etc.) can be freed for otheruses.

In addition, referring to FIGS. 2 and 8-10, the write aggregation filter(274) may create new delete notifications that cover unused areas (812)of the log file storage region (800). For example, when the unused area(812) expands to include the additional unused storage area (912)between 0 bytes and 500 megabytes, the write aggregation filter (274)can issue a delete notification covering the additional unused storagearea (912). This can provide for the same types of benefits as regulardelete notifications, even though the filesystem (210) may view theunused storage area (812, 912) as containing valid data (because theunused storage area (812, 912) is in the storage region (800) that hasbeen allocated for use by the write aggregation filter (274)). Thus, astorage device (220), such as a flash memory device, can prepare thisadditional unused storage area (912) for writing and can ceasemaintaining data that is stored in the additional unused storage area(912). This may increase the life and/or performance of the storagedevice (220), such as by decreasing the number of times that a flashmemory needs to erase a particular storage block.

Referring to FIGS. 2, 5, and 7, the write aggregation filter (274) canhave a special handshake operation with the snapshot filter (270). Inthis handshake, the snapshot filter (270) can request that the writeaggregation filter (274) copy data from a protected primary storage area(510) to a differencing file (520). Instead of sending this request downthe storage stack (200), the write aggregation filter (274) can notifythe snapshot filter (270) that the copy operation was completedsuccessfully. The write aggregation filter (274) can add the location inprimary storage (510) and the location in the differencing file (520) tothe write aggregation filter's in-memory map (730). The writeaggregation filter (274) can then redirect any read requests for thedifferencing file location to the primary storage area location, usingthe in-memory map (730). If this is done, the write aggregation filter(274) can protect the data by modifying delete notifications to removeareas that overlap with copy protected areas that have not yet beencopied. This can be done in a manner that is similar to the deletenotification modifications done by the snapshot filter (270) to protectdata, as discussed above.

If the write aggregation filter (274) receives a delete notification(260) with a flag (265) indicating that the delete notification (260)applies to the entire volume, then the write aggregation filter (274)can react differently than it would to a delete notification (260) thatapplies to less than the entire volume. For example, if the writeaggregation filter (274) receives a delete notification (260) with aflag (265) indicating that the delete notification (260) applies to theentire volume, the write aggregation filter (274) can disable itself; orthe write aggregation filter (274) can remain enabled, but cancel allongoing draining operations and delete the log file (720). If the writeaggregation filter (274) is disabled, it may remain disabled for a setperiod of time or until it is re-enabled by an action of another programand/or user input.

4. Encryption Filter

Referring to FIG. 2, the encryption filter (276) can communicate withthe write aggregation filter (274) above it and the volume managerfilter (278) below it to receive and pass on delete notifications (260)and read/write requests and data (235). The encryption filter (276) mayalso perform additional functions, such as encrypting an entire volume.

If the encryption filter (276) receives a delete notification (260) witha flag (265) indicating that the delete notification (260) applies tothe entire volume, then the encryption filter (276) can reactdifferently than it would to a delete notification (260) that applies toless than the entire volume. For example, if the encryption filter (276)receives a delete notification (260) with a flag (265) indicating thatthe delete notification (260) applies to the entire volume, theencryption filter (276) can disable itself; or the encryption filter(276) can remain enabled, but cancel all ongoing encryption operations.If the encryption filter (276) is disabled, it may remain disabled for aset period of time or until it is re-enabled by an action of anotherprogram and/or user input.

5. Volume Manager Filter

The volume manager filter (278) can communicate with the encryptionfilter (276) above it and the partition manager filter (280) in thedevice stack (250) below it to receive and pass on delete notifications(260) and read/write requests and data (235). The volume manager filter(278) can communicate with the appropriate device stack(s) (250)involved in the configuration, whether there are one or several suchdevice stacks. In addition, the volume manager filter (278) can be thePDO for the volume stack (240). Before passing on delete notifications(260), the volume manager filter (278) can convert read/write requests(235) and delete notifications (260) between volume space and devicespace.

For example, in a striping configuration, megabytes 0 to 99 of a volumemay correspond to megabytes 0 to 99 of a first storage device; megabytes100 to 199 of the volume may correspond to megabytes 0 to 99 of a secondstorage device; megabytes 200 to 299 of the volume may correspond to 100to 199 megabytes of the first device; megabytes 300 to 399 of the volumemay correspond to megabytes 100 to 199 of the second storage device, andso forth. In this example, the volume manager filter (278) can split adelete notification that applies to megabytes 49 to 150 of the volumeinto one delete notification that applies to megabytes 49 to 99 of thefirst storage device and another delete notification that applies tomegabytes 0 to 50 of the second storage device. Similar conversions canbe done for other configurations, such as where a volume spans multiplestorage devices, or where a volume takes up only part of a storagedevice. This conversion between volume and storage device space (i.e.,from volume-relative range(s) to device-relative range(s)) is an exampleof modifying the delete notifications (260). As an example of this typeof modification, consider a disk (0 to 99 megabytes) with two volumes onit, where volume 1 resides from 1 to 24 megabytes and volume 2 residesfrom 25 to 99 megabytes. If the volume manager filter (278) receives adelete notification for range 10 to 14 megabytes on volume 1, it canadjust that range to 11 to 15 megabytes, and if the volume managerfilter (278) receives the same delete notification on volume 2 (anotification for 10 to 14 megabytes on volume 2), it can adjust thatrange to 35 to 39 megabytes.

Referring to FIG. 11, in many fault-tolerant volume storageconfigurations, in addition to maintaining a primary storage volume(1110), the volume manager filter (278) can maintain redundant storage(1120), which may be used to recreate part or all of the primary storagevolume (1110) in the case of storage device failure. For example, thiscan be done with some types of redundant arrays of independent disks(RAID), such as mirroring or RAID 5. In the case of mirroring, theredundant storage (1120) includes a copy (mirror image) of a primarystorage volume (1110). The redundant storage (1120) can be created andmaintained on one or more separate storage devices. In the case of RAID5, at least three “plexes” can be used, where a plex is typically a setof one or more storage devices. One of the plexes (the redundant storage(1120)) can be an XOR of all the other plexes (the primary storage(1110)). If one of the primary storage plexes crashes, the plex can berecreated using the remaining primary storage plexes and the redundantXOR plex.

The redundant storage (1120), such as a RAID 5 XOR plex or a mirrorimage, sometimes needs to be synchronized with the primary storagevolume (1110). For example, synchronization is typically done when aRAID 5 XOR plex or a mirror image is first created, or after systemfailure, such as a dirty shutdown. Synchronization can involve thevolume manager filter (278) examining the primary storage volume (1110),comparing the primary storage volume (1110) to the redundant storage(1120), performing any necessary calculations, and writing any necessarydata to synchronize the redundant storage (1120) with the primarystorage (1110). With mirroring synchronization could include performinga series of read and copy operations; and with RAID 5, synchronizationcould include read and write operations, as well as XOR calculations.

Referring to FIGS. 2 and 11, when the volume manager filter (278) isperforming a synchronization operation with primary storage (1110) andredundant storage (1120), the volume manager (278) can omit from itssynchronization operations those areas of primary storage (1110) thathave been covered by delete notifications (260), unless subsequent writeoperations have been executed in those areas. This can be done whetherthe delete notifications (260) are received before the synchronizationoperation begins, or even while the synchronization operation isongoing. By foregoing some of these synchronization operations, storageresources can be freed.

In addition, the volume manager filter (278) can modify an existingdelete notification (260) by expanding a range of data covered by theexisting delete notification (260) to cover not only the data in primarystorage (1110) indicated by the existing delete notification (260), butalso corresponding data in redundant storage (1120).

If the volume manager filter (278) receives a delete notification (260)with a flag (265) indicating that the delete notification (260) appliesto the entire volume, then the volume manager filter (278) can reactdifferently than it would to a delete notification (260) that applies toless than the entire volume. For example, if the volume manager filter(278) receives a delete notification (260) with a flag (265) indicatingthat the delete notification (260) applies to the entire volume, thevolume manager filter (278) can remain enabled, but cancel all ongoingsynchronization operations. When the volume manager filter (278)receives an existing delete notification (260) that applies to theentire storage volume, and this is indicated by a flag (265), the volumemanager filter (278) can modify the delete notification (260) byreplacing the flag (265) with one or more delete notifications for oneor more device-relative ranges that span the entire volume beforepassing the modified delete notification(s) down the storage stack(200).

6. Partition Manager Filter

Referring to FIG. 2, the partition manager filter (280) can communicatewith the volume manager filter (278) above it and the disk class driver(282) below it to receive and pass on delete notifications (260) andread/write requests and data (235). Thus, the partition manager filter(280) can be the upper-most filter in the device stack (250). Inaddition, the partition manager filter (280) can manage the partitionsfor the associated storage device (220). If a user wants to remove thepartitions on the associated storage device (220), the partition managerfilter (280) can create a new delete notification that applies to theentire storage device (220) and pass the new notification down the diskstack to the disk class driver (282).

7. Disk Class Driver

The disk class driver (282) can communicate with the partition managerfilter (280) above it and the data verification filter (284) below it toreceive and pass on delete notifications (260), as well as read/writerequests and data (235). The disk class driver (282) can also be the FDOfor the device stack (250). If the disk class driver (282) receives adelete notification that applies to the entire storage device (220),then the disk class driver (282) can treat that delete notification thesame as other delete notifications because the disk class driver'soperations do not involve caching or transforming data.

8. Data Verification Filter

Referring now to FIGS. 2 and 12, the data verification filter (284) cancommunicate with the disk class driver (282) above it and the portdriver (288) below it to receive and pass on delete notifications (260)and read/write requests and data (235). The data verification filter(284) can perform calculations on a block of data to be written to theprimary storage (1210), and produce and store a cyclical redundancycheck (CRC) (1220) from that data. The CRC's (1220) can be used aschecksums to detect accidental alteration of data by the storage device(220). The CRC's (1220) can be stored in a CRC table (1230), which canbe stored in memory, such as RAM, or in some other storage area. Whenthe primary data is later read from primary storage (1210), the dataverification filter (284) can calculate the CRC of the data receivedfrom the storage device (220) and compare that new CRC to thecorresponding CRC (1220) stored in memory. If the stored and new CRC'smatch, then the data is verified. If the stored and new CRC's do notmatch, then the data verification filter (284) can indicate that thedata received from the storage device (220) is invalid.

The data verification filter (284) could pass on delete notifications(260) without taking other actions. If a delete notification (260)applies to a region of primary storage (1210) that corresponds to storedCRCs (1220), then the stored CRCs (1220) can get out of sync with theprimary data. That would likely not affect the integrity of the CRCs(1220) because there would be no reason for the CRCs (1220)corresponding to the deleted primary data to be read in the future.However, space in the CRC table (1230) is often quite limited,especially when the CRC table (1230) is stored in RAM. For example, insome implementations the CRC table (1230) may be limited to a smallpercentage or fixed amount of available RAM. Thus, it can beadvantageous for the data verification filter (284) to determine whetherCRCs (1220) in the CRC table (1230) correspond to data in primarystorage (1210) covered by a delete notification (260), and if so thedata verification filter (284) can delete the corresponding CRCs (1220).

If the data verification filter (284) receives a delete notification(260) that applies to the entire storage device (220), then the dataverification filter (284) can cancel ongoing operations, throw away allCRC's for the storage device (220), and start operating from scratch.

9. Port Driver

The port driver (288) can communicate with the data verification filter(284) above it and the storage device (220) below it to receive and passon delete notifications (260) and read/write requests and data (235).This communication with the storage device (220) can be done using anexisting or new protocol, such as by having a delete notificationfunction in the existing ATA protocol. If a delete notification (260) isfor a range that is greater than a maximum range that can be representedin a single delete notification protocol command, the port driver (288)can issue multiple delete notification protocol commands with adjacentranges. If the port driver (288) receives a delete notification thatapplies to the entire storage device (220), then the port driver (288)can treat that delete notification the same as other deletenotifications because the port driver's operations do not involvecaching or transforming data. If the protocol to communicate with thestorage device (220) does not include the ability to indicate that adelete notification (260) applies to the entire range of the storagedevice (220) (for example, with a flag), then the port driver (288) canmodify the existing delete notification (260) that applies to the entiredevice (220) by generating one or more delete notifications (260) withone or more adjacent ranges that describe the entire range of thestorage device (220).

Enhanced Techniques Using Delete Notifications

A. Modifying Delete Notifications in a Storage Stack

Referring to FIG. 13, a technique for modifying existing deletenotifications is illustrated. This and other techniques discussed belowcan be performed using the computing environment and componentsdescribed above or using some other environment and/or components. Anexisting delete notification can be received (1310). The deletenotification can be received from a first storage stack component in astorage stack, and can be received at a filter that is below the firststorage stack component. Upon receiving the delete notification, thestorage stack filter can determine (1320) one or more modified ranges ofdata. For example, the one or more modified ranges can be expanded orcontracted ranges, and contracted ranges can be zero ranges or rangesgreater than zero. As another example, the one or more modified rangesmay be converted ranges, such as where one or more ranges are convertedfrom volume-relative range(s) to device-relative range(s). The firststorage stack component from which the existing delete notification isreceived can be a hardware or software component in the storage stack,such as a filesystem or storage stack filter. The storage stack filterthat receives the notification can determine (1330) whether one or moreof the modified ranges of data includes a range greater than zero. Ifone or more of the ranges is greater than zero, then one or moremodified delete notifications can be passed (1340) down the storagestack to a second storage stack component, with the one or more modifieddelete notifications indicating the one or more modified ranges of data.The second storage stack component can be a hardware or softwarecomponent, such as a storage stack filter or a storage device. Moreover,if none of the modified ranges is greater than zero, the technique caninclude not passing (1350) modified delete notifications down thestorage stack.

As an example, the storage stack filter can be a snapshot filter thatcan be configured to protect stored data, and the one or more modifiedranges can be contracted to exclude one or more ranges of data protectedby the snapshot filter. As another example, the storage stack filter canbe a volume manager filter, and the one or more modified ranges can beexpanded to include data in primary storage as well as correspondingdata in redundant storage.

Referring now to FIG. 14, a general technique for creating a new deletenotification is illustrated. The technique can include creating (1410) anew delete notification with a storage stack filter below a filesystemin a storage stack. The technique can also include passing (1420) thenew delete notification down the storage stack to another storage stackfilter. For example, the delete notification can indicate redundant datamaintained by the first storage stack filter, such as redundant datamaintained by a volume manager filter. As another example, the storagestack filter can be a snapshot filter, and the newly-created deletenotification can cover snapshot data corresponding to a deletedsnapshot. As yet another example, the storage stack filter can be awrite aggregation filter, and the newly-created delete notification cancover data that has been drained from a log file maintained by the writeaggregation filter.

B. Using Delete Notifications To Free Related Storage Resources

Referring to FIG. 15, a technique is illustrated for using a deletenotification to free related storage resources. A storage stack deletenotification can be received (1510) at a storage stack filter. Thestorage stack filter can identify (1520) secondary data that is relatedto primary data covered by the delete notification and is using currentor planned storage resources. The storage stack filter can alsodetermine (1530) whether having the data continue using the resources isuseful. If so, then the storage stack filter can have the data continue(1535) using the resources. If not, then the storage stack filter canfree (1540) the resources. For example, the storage resources can be oneor more write operations, and freeing the resources can includecanceling the write operations. As another example, the storageresources can be storage space, and freeing the resources can includedeleting the secondary data to free the storage space. The primary datacould be stored in the same volume as the secondary data, or thesecondary data could be stored elsewhere, such as in RAM or in anotherstorage volume.

Referring to FIG. 16, another technique is illustrated for using adelete notification to free related storage resources. A storage stackdelete notification can be received (1610), and a storage stack filtercan determine (1620) whether a write operation is rendered obsolete bythe delete notification. If so, then the write operation can becancelled (1630). If not, then the write operation can continue if theoperation is ongoing, or continue to be planned if the operation isplanned for the future (1640). The write operation could be, forexample, part of a lazy write operation or part of a synchronizationoperation.

C. Delete Notifications for an Entire Storage Volume

Referring to FIG. 17, a technique is illustrated using deletenotifications that apply to an entire storage volume. A deletenotification can be received (1710) at a storage stack filter in astorage stack. It can be determined (1720) whether the deletenotification applies to an entire storage volume, such as by examining aflag in the delete notification. If the delete notification does notapply to the entire storage volume, the storage stack filter can take(1730) a first set of actions in response to the notification. If thedelete notification does apply to the entire storage volume, then thestorage filter can take (1740) a second set of actions in response tothe notification. The notification can also be passed (1750) down thestorage stack. This technique can be repeated for multiple storage stackfilters in a storage stack. Such a notification, which applies to anentire volume, can be issued by a reformatting component that is able toreformat the volume or by some other component. The second set ofactions can include actions such as disabling the filter and/or deletingunnecessary secondary data files. For example, the storage stack filtercould include a snapshot filter and the second set of actions couldinclude deleting all snapshots managed by the snapshot filter anddisabling the snapshot filter. As another example, the storage stackfilter could include a write aggregation filter, and the second set ofactions could include disabling all lazy writes to the volume that aremanaged by the write aggregation filter.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

1. A computer-implemented method, comprising: receiving a storage stackdelete notification at a storage stack filter, the delete notificationindicating deletion of primary data in a primary storage region; inresponse to the delete notification, performing acts comprising:identifying secondary data that is taking up storage resources managedby the storage stack filter, the secondary data being associated withthe primary storage region, and the storage resources being resourcesother than the primary storage region; determining whether to have thesecondary data continue taking up the storage resources; and if thesecondary data is not to continue taking up the storage resources, thenfreeing the storage resources.
 2. The method of claim 1, whereindetermining whether to have the secondary data continue taking up thestorage resources comprises determining whether access to the secondarydata may be requested in normal computing operations.
 3. The method ofclaim 1, wherein the storage resources comprise a data write operationand freeing the storage resources comprises canceling the data writeoperation.
 4. The method of claim 3, wherein the data write operationcomprises a planned data write operation.
 5. The method of claim 3,wherein the data write operation comprises an ongoing data writeoperation.
 6. The method of claim 1, wherein the storage resourcescomprise a secondary storage region of a storage device.
 7. The methodof claim 6, wherein the secondary storage region and the primary storageregion are in the same storage volume.
 8. The method of claim 6, whereinthe primary storage region is in a storage volume and the secondarystorage region is not in the storage volume.
 9. One or morecomputer-readable storage media containing one or more programs, the oneor more programs comprising instructions that are executable by acomputer system to perform acts comprising: receiving a storage stackdelete notification indicating a range of invalid data; determiningwhether a write operation is rendered obsolete by the deletenotification; and if the write operation is rendered obsolete by thedelete notification, then canceling the write operation.
 10. The one ormore computer-readable media of claim 9, wherein the write operation isa lazy write operation.
 11. The one or more computer-readable media ofclaim 9, wherein the write operation is part of a synchronizationoperation that synchronizes primary data and redundant datacorresponding to the primary data.
 12. The one or more computer-readablemedia of claim 11, wherein the synchronization operation synchronizesdata in a RAID array.
 13. A computer system comprising: a primarystorage region of a storage device storing primary data; a secondarystorage region that is different from the primary region, the secondaryregion storing secondary data corresponding to the primary data; and astorage stack filter that is configured to receive a storage stackdelete notification indicating deletion of at least a portion of theprimary data, and to delete the secondary data in response to the deletenotification.
 14. The computer system of claim 13, wherein the storagestack delete notification is a first storage stack delete notification,and wherein deleting the secondary data in response to the first deletenotification comprises issuing a second storage stack deletenotification indicating the secondary data.
 15. The computer system ofclaim 13, wherein the primary region and the secondary region are in onevolume.
 16. The computer system of claim 13, wherein the secondaryregion is in memory.
 17. The computer system of claim 13, wherein thesecondary data comprises a checksum of at least a portion of the primarydata.
 18. The computer system of claim 13, wherein the secondary datacomprises redundant data corresponding to the primary data.
 19. Thecomputer system of claim 18, wherein the redundant data is stored in aRAID array.
 20. The computer system of claim 18, wherein the secondarydata comprises snapshot data.